flory



Jan. 31, 1956 E, FLQR 2,733,364

MAGNETIC BEAM;F'OCUSING SYSTEMS Filed March 22, 1951 2 Sheets-Sheet 1 '9 wa e 52 a 0on0 11 I!) INVENTOR leggz'e EH01 y L. E. FLORY MAGNETIC BEAM-FOCUSING SYSTEMS Jan. 31, 1956 2 Sheets-'Sheet 2 Filed March 22, 1951 INVENTOR Zeslze E1701 9ATTORNY I 2,733,364 MAGNETIC BEAM-FOCUSING SYSTEMS Leslie E. Flory, Princeton, N. 1., assignor to Radio Corporation of America, a corporation of Delaware Application March 22, 1951, Serial No. 216,857 14 Claims. (Cl. 313-45 This invention relates to magnetic-focusing and beamalignment systems for electron-beam tubes and, though not necessarily limited thereto, will be described as applied to a television camera tube of the so-called Vidicon variety.

Vidicon photo-conductive television cameras are de scribed in an article beginning on page 70 of the May 1950 issue of Electronics, and in copending U. 8. applications: Serial No. 204,045 of S. V. Forgue, filed January 2, 1951, now U. S. Patent 2,710,813 and Serial No. 212,550, of P. K. Weimer, filed February 24, 1951, now U. S. Patent 2,687,484.

The pickup tube used in this camera features a photoconductive target, as distinguished from the photo-emissive targets of the iconoscope and orthicon. The greater sensitivity of pht0-c0nduct0rs as a target material peraddition, a slight adjustment of the direction of the field in the region of the gun is necessary in order to compensate for possible misalignment of the gun and the field.

This focusing and aligning has hitherto been accomplished by a solenoid, surrounding the entire Vidicon from in direction and intensity. I The power consumption of these focusing and aligning coils is about 4 ratus necessary; and dissipation of causes an undesirable heating of the Accordingly,

simplify the construction, and of assembly of television pickaccomplished in accordance with a preferred embodiprovide an improved television.

. '70 The .above. mentioned, and other related objects, are

glass supporting surface.

2,733,364 Patented Jan. 31, 1956' the electron beam. Alignment of the beam as it leaves accelerating, focusing and deflection fields, is accomplished by means of ad ustable slugs These slugs are adjusted to shift the flux of the magnetic'field in the direction and to the extent necessary to accomplish proper alignment of the is described in greater detail in conaccompanying two sheets of drawings,

Fig. 2 is an end view of the device of Fig. 1;. Fig. 3 is a side elevation, partly in section, of the device of Fig. 7 target end of the structure; Fig. 4 is a similar view of the assembly, justable slugs on the magnetic focusing rods the electron beam; Fig. 5 is a view similar to Fig. 4 showing another form' of beam-aligning mechanism; Fig. 6 is a vertical section structure similar to the ones showing adfor aligning of one end of a magnetic shown in the other figures plate 29 of the tube 11. terial which is light-transparent and electrically-conducto application in athin film upon a Aluminum may be used. The layer 27 is comprised of selenium or one of the or selenides, which are normally insulators but become The references suitable materials.

The inner surface of the tube 11 is covered by an electrically conductive coating 31 in the-area between the electron beam source 13 and the target '15. This conductive coating terminates in a wire mesh screen 33 across the tube in the vicinity of the target 15.

tooth generator of line scansion frequency, and the other saw-tooth generator of frame" scansion frequency. These saw-tooth generators are wellknown'in' the art-and" are not shown.

Under a preferred set of operating conditions: the cathode 19 is at ground potential; the controL electrodev ZTi's' at' a negative 30 volts; the accelerating electrode. 23. is'at apositive 360 volts; the conductive. coating 31 and. the screen 33"electrically connected thereto areat aposi= tive- 2.00. volts; and the conductive film 25 of the target 'is1at a positive 10 to. 30 volts.

In the operation of the tube,. the electron beam 43- emerges from an aperture 45in the accelerating electrode 23. and is caused by voltages applied. to the. coils of. the deflection yoke 35 to scan animage raster upon thephotoconductive layer 27 of'the target. 151.

Bombardment of'the surface of the photo-conductive layer 27 brings it to the potential of the cathode, 19. Secondary electrons released'by the bombardment arev collected by the wire mesh 33 and the conductive coating 31. The effect of this. bombardment. of the surface of'the' photo-conductive layer 27 is-to produceta condition of electro-static charge across the photo-conductive layer 27'between the bombarded surface and the metal film 25 which is approximately. 10. to 3.0. volts above cathode potential.

When a scene to be televised is focused through the glass face 29' of the tube upon the. target, assembly 15, it rendersthelayer, 27 conductive in the areas where light strikes. it. The extent to whichit becomes. conductive in each particular area is determined by the intensity of the lightimage in that area. When. layer. 27 under the: influence of the extents in variousparts. of itstotal area, it causes a dischargeof. potential from. the. bombarded surface of. the

layer-:27 to theconductive film. The.layer.27, under the influence, ofjlight,.,becomes;conductive. only in a direction substantially parallel to the. light .rays. thatimpinge upon; it, andnot in. a lateral. or. crosswise .directiom Consequently,

layer 27,.which faces theelectron beam. 43, is one ofunevenelectrical potential. The entire surface'has. become whatmightbe termed. an electrorstatic. image of the sceneto betelevised.

As, the electronbeam to-conductive layer.

43 scans the surface of the: phocauses an. electronflowthrough the; to theconductivefilm 25.. The: extent.

originalf. potential. output resistor. 47.

to .whi'chthe original chargeleaked throughzthe -photo-.- conductor27 under the influence of lightfrom the-scene;-

to. be. .televiseddeterminesthe amount of electron. currentthat will. be, necessary: to. restoreathe-original potential; andvariations. in. this current throughdhe condenser :49.

as the electron beam scans a complete rasterrbecomwther video. output of. the tube;

electron. beam. 43, as: it travelsjromrit'stsource 13.

to ,the target assembly 15,.isi mamtained; in properyfocus:

a rectangle; about; the. outside..of;.the;tube.=. These rods:-

areheld in. placehy two. sofhironend;plates 39:and 39; asshown. in Fig. 2.-.

Asshown. tit-Fig.3; a..-soft+.iron magnetic shield 51 is= plate. 39. It is. connected: to. the end'platez39fi the.- .accelerating. focusing; and

light image becomes conductiveto variousthe resulting. conditionupon the surface. of the 27, in this. uneven. condition of .elec:- tron. charge whichthas just been described, it; restores; the particular. area under bombardment to cathodeepotens tiall', Thisrestoration. of the surface of. the layer 27 to. its:

provided. in the area. of. the:' target assembly: 15;; The shield.51 is cylindrical .intshape and is..of:a diameter largers than boththe envelope 11. and-,thetopening 53th: the end and; by furnishing .a. path. for: theaflux: fromgtheamagnetizedzrods-- 41; it prevents. radial-field: lines from zdi stortingsthedocus offth'mbcamandprovidesratrmagneticfield.iwhiclrdszmoww nearly longitudinal. and garallchto; theseaxiszoftthczstuber The... electron beam: asedt leavesetheegunnshouldz enter deflecting; fields'r substanttially at the axis of the tube and from a direction normal to these fields. Things such as stray magnetic fields or mechanical misalignment of the gun interfere with this requirement and make some method of beam alignment" necessary.

Fig. 4 shows a preferred method, in accordance with the invention, for aligningthe' electron beam with the focusingfield as it leaves the electron gun or source 15. This alignment is accompanied by the use ofsmallslugs" of magnetic material, (f. e; azmaterial.which.ofiers;a.rela1 tively low reluctancerpathttomagnetic flux, such asiron) These slugs are adjusted to shunt the flux of the magnetized rods and asymmetrically distort their-fields to produce a shift in'the:direction desired. In the particular embodiment shown in Fig. 4 the shunting slugs comprise soft iron cylinders 55 mounted for slideable movement along the magnetized rods 41 and adapted to be maintained in any selected position by means: of-i set screws .57.

Fig. 5 shows an. alternative. type of. alignment. slugtf In. .thisqembodiment, brass cylinders. 59 form..a continua? tion of an end of the magnetized rods 41. Thesecylim ders 59 are. equipped with threaded recesses intowhich iron screws 61 are adjustablysecured; Theiron screws; 61, as; they are workedin. toward the magnets 41,,reducer the; non-magnetic gap. within the. cylinders 59 so' that by: a non-symmetrical. arrangement of the; positionsofa the screws the direction of the field can the desired correction for alignment.

In. the. embodimentv shown, in, Fig. 6, alignment. oi the electronbeam is accomplished by ironscrews;63. secured. in. brass. blocks 65. which have. appropriate; threaded. recesses and arewelded to the. endplate. 39. Asascrew 63, is worked closer to-the tube, a concentration. of flux occurs inthe. vicinityof the screw. The resultis an asym-.--

soft iron. These angle irons are secured tothe corners:

of theendplates 39 and 39' and. are;parallelland inzclose." proximity to the magnetized rods. 41 which are adapted: to beareceived inholes. 69in theend plates;39 and'.39.". The function of the angle irons or strips 67 is to furnish a. shunt path for the; flux of; the, magnetizedarods; 41, and. thereby to. furnish a means forrregulatingq the,=:in=. tensity of. themagnetic field. acting upon. ther electron beam 43.. The.factv that the. thicknessand width: ofrthe: angle. iron. 67 can bearather-easily varied makesaittun. necessary to demand exactitude in the.field.:strength ofwthes= magnetsused for. the rods 41..

From. the; foregoing; .it..wil1. now be: apparent that presentinvention provides: a; simple; inexpensive, and

trouble--freetheamz focusing and alignment system; suit ablefor .usezin; connectiomwithtVidiconandother cathode ray tubes;

1. The methodiof controllingan electron beam whichcomprises; establishingm permanent magnetic;field=having-lines of force extending. substantially.-para1lel to and" bly -oizmagnetized 'rod's mounted inspacedrelation about be-warpedto: give-.

the. infiuence' of: said magnetic fierc the contour of said lines of means for accelerating said beamtoward' saide' and substantially parallel to said electron rality of adjustable beam, a pluends of said target, and strips of magnetic material in shunt relation to said magnetized rods.

4. An electron discharge apparatus comprising means for producing a beam of electrons along a path, a target for said beam of electrons mounted transversely to said beam path, an assembly of magnetized rods mounted in spaced relation about and substantially parallel to said electron beam path for establishing a focusing field for said beam, and auxiliary magnetic shunt means positioned adjacent to said rods for shunting a portion of said field and for changing the contour of said focusing field, said shunt means comprising a plurality of slugs of magnetic material adjustably mounted on said magnetized rods.

6. An electron discharge apparatus comprising means for producing a beam of electrons along a path, a target for said beam or electrons mounted transversely to said material adjustably mounted in recesses adjacent'to the ends of said magnetized rods.

7. Apparatus for controlling an electron beam pro- 8. Apparatus for controlling an electron beam along a path, said apparatus comprising an assembly of magnetized rods supported about an axis and adapted to be mounted in spaced relationship about and substantially parallel to the beam,

yoke, and means supporting said yoke coaxially about said axis and Within said rod assembly.

10. Apparatus for controlling an electron beam along a path, said apparatus comprising an assembly of magnetized rods supported about an axis and adapted to be parallel to the path of said beam, a tubular deflecting yoke Within said rod assembly,

and a tubular envelope ccaxiaily supporting said yoke about said axis.

11. A television camera tube comprising an electron gun for producing and accelerating a beam of electrons along a path, a photosensitive target mounted transversely to said beam path, beam deflection means between said References (Iited in the file of this patent UNITED STATES PATENTS FOREIGN PATENTS Great Britain Sept. 13, 1937 

